Osmotic stress in Synechocystis sp. PCC 6803: low tolerance towards nonionic osmotic stress results from lacking activation of glucosylglycerol accumulation

Abstract

In order to compare the molecular principles of the acclimatization of bacterial cells to salt and nonionic osmotic stress, the moderately halotolerant cyanobacterium Synechocystis sp. PCC 6803 was challenged by salt (NaCl), and the osmolytes sorbitol and maltose. The physiological response towards each of the three compounds was found to be different. After salt addition, the cell volume remained unchanged, and the accumulation of the osmoprotective compound glucosylglycerol (GG) was observed after activation of the key enzyme GgpS at the biochemical and gene (ggpS) expression level. Sorbitol addition had only minor effects on the cell volume. In spite of the fact that the ggpS expression was increased, the GgpS enzyme was not activated, resulting in the absence of GG accumulation. In contrast the cells accumulated sorbitol, which served as a compatible solute and assured a certain osmotic resistance. In comparison to NaCl and sorbitol, the addition of maltose caused a strong decrease in cell volume indicating water efflux. However, no osmolyte accumulation was observed, resulting in an osmosensitive phenotype. Consequently, a successful response of Synechocystis cells to an osmotic challenge is indicative of the de novo synthesis of GG upon salt-dependent activation of the GgpS enzyme or the uptake of external solutes.

Comparative Analysis of kdp and ktr Mutants Reveals Distinct Roles of the Potassium Transporters in the Model Cyanobacterium Synechocystis sp. Strain PCC 6803

“…During the second phase of cell adaptation, not only the biosynthesis and accumulation of the compatible solute but also an influx of sorbitol into the cells may have occurred. Sorbitol influx has been shown to occur in cells of wild-type Synechocystis and a mutant unable to synthesize the compatible solute glucosylglycerol when they were treated with large amounts of external sorbitol (49). Taken together, these results suggest that the uptake of K ϩ into the cells via K ϩ transporters was required for the first phase of recovery and that Ktr especially but not Kdp contributed significantly to this first recovery phase.…”

Boosting Autofermentation Rates and Product Yields with Sodium Stress Cycling: Application to Production of Renewable Fuels by Cyanobacteria

“…For example, in Synechocystis sp. PCC 6803, it was shown that the response to solutes used to induce hypertonic (hyperosmotic) stress differs depending on the identity of the solute used (18). Although the same systems are involved in transduction of salt signals and hyperosmotic signals, expression of individual genes is regulated to different extents when using sodium chloride versus sorbitol in this organism (21).…”

Aquaporin AqpZ Is Involved in Cell Volume Regulation and Sensitivity to Osmotic Stress in Synechocystis sp. Strain PCC 6803

“…It has been reported that Synechocystis regulates Na ϩ influx and efflux across the plasma membrane and the thylakoid membrane via an Na ϩ transport system, e.g., an Na ϩ /H ϩ antiporter, in order to control ion homeostasis in the cytosol (11,21,33,48). In addition to the Na ϩ cycling system, NaCl also induces synthesis of the osmolyte glucosylglycerol in Synechocystis (27). A reduction in the amount of AqpZ protein was observed during salt stress (Fig.…”